Mattress



FIG. 1 is a top, front and left side perspective view of a mattress, showing my new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a left side perspective view thereof; and,

FIG. 4 is a front side perspective view thereof.

The bottom, right, and rear side view are omitted because they are identical with the top, left and front view, respectively. 

CLAIM The ornamental design for a mattress, as shown and described. 